The amount of water flowing in a river system forms a tiny percentage of the total water. Oceans hold approximately 1370 million cubic kilometers of water, which reflect to about 97% of the Earth’s total water.
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Seventy five percent of the Earth’s fresh water is in the form of land ice while most of the remaining percentage is found in ground water. The lakes constitute about 125,000 cubic kilometers of the Earth’s water while the rest is found in soil moisture, the atmosphere and rivers, with the biosphere containing the least amount of water on the Earth’s surface.
Rivers, streams and Lakes
The words river and stream are used interchangeably in technical writing though they mean different things. While a river refers to a surface flow of water in a channel, the concept of a stream does not involve flow in a channel. Other terms used to signify small natural watercourses include creek, branch, burn and brook. Rivers are subjected to water loss through seepage and percolation into nearby aquifers.
They also lose water through evaporation. As a result, the ability of a river or a stream to survive is dependent on the balance between water input and water loss. This paper looks at the various geographical elements of rivers, as well as, their relation to other water bodies and particulate matter.
Water is in a constant cycle through various systems including river channels, ground water, lakes, soil and land ice. Oceans experience more evaporation than precipitation.
As a result, the net difference of water vapor is conveyed over land, where it precipitates as rain. About 30% of the rainwater finds its way back to the ocean through river runoff and another 6% as direct discharge from ground water. Some of the rainfall is stored in other water bodies like lakes and rivers.
The techniques used to compare rivers in the world involve an analysis of the size of the drainage area, the length of the main stem and the mean discharge. Research suggests that the global mean of the external runoff is approximately 0.01m3/s/km2.
The biggest rivers in the world are also known to have high discharges. They get their water from convectional rainfall in the equatorial region, or monsoon rains that are influenced by altitude.
Streams are classified as perennial, intermittent, or ephemeral. Intermittent streams can be either temporal or spatial and are mostly found in karstic areas. The ephemeral streams only flow when the ground water table is raised by episodes of heavy rainfall.
During this period, they reactivate various existing outlets that are located above ground, causing heavy erosion, as well as, deposition of large amounts of soil and rock materials.
Particulate matter in rivers
Rivers run through different courses between their source and discharge. The upper course refers to the highest section of a river, which is marked by hills or mountains. The water flows steeply into the middle course, where the gradient is less steep, allowing meanders to form.
The lower course is characterized by level ground, meanders, oxbow lakes and deltas as the river reaches open water for discharge. The flow of a river can be either laminar, where the water flows at low velocity, or turbulent, where the water flows at high velocity.
Rivers are characterized into perennial and non-perennial. Perennial rivers include permanent rivers, which flow all year round, and exotic rivers, which also flow consistently despite running through a desert, like the Orange River, and the Nile. Non-perennial rivers can be either periodic or episodic.
Periodic rivers only flow in certain seasons after a period of rain. Episodic rivers, on the other hand, flow after an episode of rain, such as a thunderstorm. While periodic rivers flow for several months, episodic rivers may flow for a few hours or a few days or weeks at most.
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Rivers transport various substances including dissolved matter, solids, such as igneous, metamorphic and sediment rock, and suspended loads, like silicon and aluminum found in the soils.
Rivers deliver about 100 times more rock debris to the sea than coastal erosion, though the rate of erosion and transportation varies for different rivers. The dissolved substances are added to the oceanic salt, though rivers have limited amounts of dissolved substances.
Examples of rivers around the world
Rivers have many uses to human beings and other living organisms. They also serve a significant purpose in the ecology of wetlands. Some of the most prominent rivers in the world include the Sepik River, Mississippi River, Volga River, Zambezi and Mekong River. The Sepik River is the longest river in Guinea, with a length of 1126 km. It originates in the central highlands and drains in the sea, without forming a delta.
The Mississippi River is about 3730 km long and is the largest river in North America, passing through 31 US states. It originates at Lake Itasca and drains in the Gulf of Mexico. The Volga River is the longest river in Europe with a length of 3645 km. It is a crucial river in Russia as it serves 11 of its biggest cities.
The Volga River has its source in the Valday Hills and drains in the Caspian Sea. River Zambezi is the fourth largest river in Africa, extending for 3540 km from the black wetland in Zambia through Angola, Namibia, Botswana and Zimbabwe, before draining in the Indian Ocean from Mozambique. River Zambezi is a significant wildlife habitat for various animals including crocodiles and hippopotamuses.
The Mekong River has a length of 4350 km, which makes it the 12th largest river in the world. The river originates in the Tibetan Plateau and flows through China, Thailand, Cambodia and Vietnam. It has many rapids and waterfall, which limit navigation. The Ganges River is 2510 km long. It starts in the Himalayas, in India, and discharges its water in the Sunderbans delta.
It serves a religious purpose for the Hindus. Danube is a significant river in Europe. It is the second longest river after Volga, flowing for a length of 2850 km. Danube marks the border of 10 European countries starting in Germany and draining in the black Sea.
Yangtze River is about 6300 km long, which makes it the third largest river in the world, and the longest river in china. It flows from a glacier in the Tibetan plateau to the East China Sea. It serves the three gorges Dam, which is the world’s biggest hydroelectric power plant.
The Nile is the longest river in the World. It extends for a length of 6650 km from east Africa to the Mediterranean. The river is a vital source of water in Egypt, which depends on the annual silt depositions for farming wheat and other crops.
Amazon River is the second longest river in the world. It is also regarded as largest river in the world on the basis of its volume. The river is 6400 km long and flows through various countries in South America including Peru, Colombia, and Brazil. It then discharges into the Atlantic Ocean.